If you are a Small Business customer, find additional troubleshooting and learning resources at the Support for Small Business site.

You are connected to a corporate wireless (also known as Wi-Fi) network or are signed in to a Microsoft Office 365 subscription that's enabled for single sign-on (SSO) by using Active Directory Federation Services (AD FS) 2.0. When you try to sign in to Microsoft Lync Mobile on your Apple iOS-based device (such as an iPhone or iPad), you receive one of the following error messages:

Can't verify the certificate from the server. Please contact your support team.

Can't connect to the server. It might be unavailable. Also please check your network connection, sign-in address and server addresses.

In addition, when you view the Lync Mobile logs for iOS, you see the following entry:

Note The Apple iPhone Configuration Utility must be downloaded by using a Windows-based or Mac-based computer.

As soon as the application is installed, start the utility, and then click Configuration Profiles.

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In the upper-left corner, click New to create a Configuration Profile. Start by naming the profile. In this example, Contoso Root Certificate is used, and the unique identifier is set to com.contoso.cert.profile. Complete the General settings by entering your company name and optional description.

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Browse to the certificate icon that's labeled Credentials, and then click Configure.

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A list of certificates that are found on your local computer will be displayed. Assuming that your computer trusts your internal local area network (LAN) certificates, your root certificate will be shown here. Scroll to the correct certificate, and then click OK.

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The certificate will be shown in the Credential window, and all changes are immediate. For small or single installations, connect your device to your computer by using a USB cable. The device will be displayed in the Configuration Tool under DEVICES. Select the device, and then click the Configuration Profile tab.

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There's an option to install the profile directly. Click Install to start the process. On your device, an Install Profile window appears, and you must click Install followed by Install Now to confirm the installation of the Root Certificate. If you have a password, you'll have to enter it, and then click Done.

The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.